So, right now I've got a Brenspeed tune and an SCT Xcal 3. I'm looking at getting 3.73's put in and have a question. I know that I can use the Xcal to correct the speedo for the new gears, but what happens if I return to stock tune for emissions/warranty work? Am I able to correct the rear end ratio setting with the Xcal without affecting anything else in the factory tune?

 

I just put 4.10s in my Bullitt, and I asked Chandler at Brenspeed the same question. He said that the ratio change is made by selecting an 'option' at the time you load a custom tune. When you return the car to stock tune, the stock ratio comes back too.
You cannot load the axle change by itself on top of the stock tune.


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